Microgrooves with Small Taper Angle Processed by Nanosecond Laser in Closed Flowing Water.

To improve the capability of nanosecond lasers to process structures with a high aspect ratio, a new method of nanosecond laser processing in closed flowing water was proposed in this paper. The microgrooves on a stainless steel 304 surface were processed by the new method, and the influence of processing parameters on the microgrooves was studied. The comparative experiments of laser processing in still water and overflowing water were also carried out, and the unusual phenomenon of laser processing in different flowing water was discovered by a high-speed camera. The results showed that the flowing velocity played a crucial role in underwater laser processing, and that high flowing velocity could timely remove bubbles in closed flowing water, thus obtaining higher processing efficiency. As the depth of the groove increased, the bubbles firstly affected the processing of the sidewall, causing a circular transition between the sidewall and bottom surface. The reflection of the laser beam by the bubble could cause secondary processing on the sidewall, resulting in a decrease in the taper angle. Based on the above research, the microgroove with a width of 0.5 mm, aspect ratio of 3, and taper angle of 87.57° was successfully processed by a nanosecond laser in closed flowing water. Compared to conventional nanosecond laser processing, laser processing in closed flowing water was more advantageous in processing microgrooves with a small taper angle and high aspect ratio.

Finite-time trajectory tracking control of quadrotor UAV via adaptive RBF neural network with lumped uncertainties.

The trajectory tracking control of the quadrotor with model uncertainty and time-varying interference is studied. The RBF neural network is combined with the global fast terminal sliding mode (GFTSM) control method to converge tracking errors in finite time. To ensure the stability of the system, an adaptive law is designed to adjust the weight of the neural network by the Lyapunov method. The overall novelty of this paper is threefold, 1) Owing to the use of a global fast sliding mode surface, the proposed controller has no problem with slow convergence near the equilibrium point inherently existing in the terminal sliding mode control. 2) Benefiting from the novel equivalent control computation mechanism, the external disturbances and the upper bound of the disturbance are estimated by the proposed controller, and the unexpected chattering phenomenon is significantly attenuated. 3) The stability and finite-time convergence of the overall closed-loop system are strictly proven. The simulation results indicated that the proposed method achieves faster response speed and smoother control effect than traditional GFTSM.

Visualized concentration sensors based on fluorescence indication in a dye-doped polymer microwire.

We demonstrate visualized microwire sensors based on fluorescence indication for detecting the concentrations of the aqueous solutions. The single Rhodamine (RhB) doped polymer microwires (PMWs) which are excited by the waveguiding excitation method are used as the sensory area. According to the fluorescent microimages of the PMWs, stable periodic oscillations could be observed in the RhB-doped PMWs. The fluorescent period which is dependent on the concentration is further analyzed by image processing and information extraction algorithms. Corresponding to a 1.0% change, the period length change of the visualized sensor reaches ∼380 nm, ∼270 nm, and ∼300 nm in NaCl, KCl, and sucrose solutions, respectively. The dection limits of the three solutions are estimated to be around 1.5 × 10-4%. The dye-doped PMW sensors by fluorescence indication and image analysis proposed here realize the direct visualized detection in concentration sensing, making it possible to avoid the challenges of stability and weak signal detection and offer a potentially stable and cost-effective approach for micro/nanofiber sensor application.

Diagnosis and treatment of tuberculosis in adults with HIV.

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), continues to pose a major public health problem and is the leading cause of mortality in people infected with human immunodeficiency virus (HIV). HIV infection greatly increases the risk of developing TB even before CD4+ T-cell counts decrease. Co-infection provides reciprocal advantages to both pathogens and leads to acceleration of both diseases. In HIV-coinfected persons, the diagnosis and treatment of tuberculosis are particularly challenging. Intensifying integration of HIV and tuberculosis control programmes has an impact on reducing diagnostic delays, increasing early case detection, providing prompt treatment onset, and ultimately reducing transmission. In this Review, we describe our current understanding of how these two pathogens interact with each other, new sensitive rapid assays for TB, several new prevention methods, new drugs and regimens.

Experimental investigations into the performance of die-sinking mixed-gas atomization discharge ablation process on titanium alloy.

As a variant of highly efficient electrical discharge machining (EDM), the die-sinking mixed-gas atomization discharge ablation process (DMA-DAP) uses an atomized dielectric formed by a mixed gas, which mainly composed of oxygen and supplemented by nitrogen, and water medium as the discharge medium. In this technology, the oxygen in the medium is used for exothermic oxidation, and the vaporization and explosion of the water generates a chip removal force for highly efficient erosion. The present work uses single-factor tests to compare the characteristics of processing the difficult-to-machine material titanium-alloy special-shaped cavities using either DMA-DAP or EDM. The current, pulse width, pulse interval, and dielectric pressure are selected as the single-factor processing parameters, and how they influence the material removal rate (MRR), electrode relative wear rate (ERWR) and the surface morphology of the processed square cavities is analyzed. The results show that with DMA-DAP, the MRR is more than 12 times that of EDM, the ERWR is reduced by more than 98%, and the surface morphology is relatively good. Finally, taking an aero-engine radial diffuser as the profiling object, DMA-DAP realizes a profiling sample in the form of a variable-cross-section cavity that EDM cannot process, and the efficient die-sinking processing ability of DMA-DAP is verified.

Experimental Research on Deep-And-Narrow Micromilled Grooves Using a Self-Fabricated PCD Micro-Cutter.

Deep-and-narrow micro-grooves are the common functional structures of miniature parts. The fabrication of the micromilled grooves with high quality and accuracy is the essential guarantee of the causative performance for these miniature parts, and micromilling is the most versatile process to machine such micro-grooves. However, micromilling technology is a highly tool-dependent process, and the commercial carbide micromilling cutter has shown obvious deficiencies in terms of rapid tool wear and inferior machined quality during the machining process. In this paper, a polycrystalline diamond (PCD) micromilling cutter with a large-aspect-ratio (LAR) was designed and prepared by the self-proposed hybrid fabrication method of laser and precision grinding. Micromilling experiments on oxygen-free copper were conducted, and the carbide micromilling cutter was selected in the comparative experiments. The variations of milling forces and specific energy were analyzed through the parameter experiments. Then, the surface quality, machined accuracy and tool wear were further investigated. Results showed that the PCD micromilling cutter with an aspect ratio of 3.25 was successfully manufactured by the proposed hybrid method. The self-fabricated PCD micromilling cutter presented remarkable superiority in terms of the surface quality, machined accuracy, and tool wear when preparing deep-and-narrow micro-grooves. Finally, a satisfactory micromilled groove with an aspect ratio of 2.5 was achieved with the self-fabricated LAR PCD cutter under the optimized conditions.